When is invoke required on GUI objects?

Question

Using C# Windows.Forms, do the methods Invalidate(), Refresh(), etc. have to be run on the main/GUI thread (require Invoke/BeginInvoke)? How about changes to members of a GUI object such as adding/deleting Points or changing the Color of a Series in a Charting.Chart object?

I have some of these changes occuring in a worker thread without any issues (so I guess they are ok?), but I'm trying to distinguish which changes are explicity required on the GUI thread and which changes can occur on the object in a worker thread. Does anyone have a link or book reference to guidance on this subject?

Classes can be thread-unsafe without them telling you so explicitly with an exception. The List<> class would be an example. Only ever use members of a class whose instance was created or members accessed on another thread when the docs tell you that the member is thread-safe. It is quite rare, the Chart class certainly isn't. This is not something you 'risk', the cost of guessing wrong is huge. — Hans Passant, Apr 05 '11 at 16:54

score 4 · Accepted Answer · answered Apr 05 '11 at 16:17

In general, you should typically assume that ALL changes to GUI elements should be made on the UI thread.

Often, changes on a background thread will work during testing, but break post-deployment. In general, unless otherwise documented, it's much safer to assume that everything should be on the UI thread.

score 1 · Answer 2 · answered Apr 05 '11 at 16:18

You can not make synchronous method calls that manipulate WinForms controls on a worker thread.

I'm not sure what "adding/deleting Points" is referring to, or the Charting.Chart class. This class may encapsulate GUI Thread invocation on their own.

Generally speaking, if you are modifying the size, text, background color, or other properties on a Control, this must use Invoke / BeginInvoke.

score -1 · Answer 3 · answered Apr 05 '11 at 16:17

-1

This should tell you Control.InvokeRequired

answered Apr 05 '11 at 16:17

František Žiačik

7,511
1
34
59

That just tells you whether you're currently on the UI thread, not whether a specific API requires this. – Reed Copsey Apr 05 '11 at 16:18
That just tells you if you are on the wrong thread. It doesn't tell you if the method you are about to call is going to need to be run on the window handle's thread. – David Heffernan Apr 05 '11 at 16:18
@Reed Copsey: only if it has handle created – František Žiačik Apr 05 '11 at 16:21
šek: Yes - but it still doesn't answer the OP's question. It has nothing to do with whether a specific method or property requires this. – Reed Copsey Apr 05 '11 at 16:27

When is invoke required on GUI objects?

3 Answers3

Linked

Related